I wonder how the other religions would answer the question? My guess is that it would sound much the same.
But there is another answer. One that you probably won't hear from a Christadelphian. The fact that there are so many religions makes perfect sense if they are all man-made. If no holy book was ever divinely inspired, then we are just seeing the same human phenomenon repeat itself in different ways. This is not a new concept. Most believers already accept that all other religions are mistaken. Why not apply that same skepticism to their own beliefs too? Why should someone like me believe that all of the other religions are false, but this one over here (that looks indistinguishable from the others in almost every respect) is totally true?
Interpretation
One reason there are so many different brands of Christianity is because different people understand things differently. The result of this is that even though they read the same words, there is no one single interpretation. There are many different interpretations, and some of them are contradictory. Contradictions are not surprising at all in this view. In fact they should be expected. Even if there is only one “correct” understanding of an ancient text, it seems that that particular understanding will be inaccessible to us. We may well hold the correct understanding ourselves, but how shall we know for sure? Who among us has any authority to claim that our interpretation or our understanding outshines anyone else's? Where there are disagreements over interpretations, how shall we decide who is right?
Without a divine tap on the shoulder, or some way to empirically test the results, any search for the “one true interpretation” of any ancient scripture seems misguided. At best we can only hope to reach a consensus. Is the interpretation upon which the largest number of people agree guaranteed to be the correct one? The flaws in such a view are obvious. The fact is that we don't know. We can't know, at least not in any absolute sense. Perhaps seeking a consensus is the best we can do, but even that is not always possible. Any claim to the correct interpretation of a passage must be accompanied by a measure of uncertainty.
This being the case, is it fair to judge those who disagree with us, as heretical, and cast them out from our midst? Suppose their view later became the majority view. What then? Examples of such shifts in the consensus or majority view abound throughout history, and yet even today people still find themselves shunned by their former friends and family, over a disputed belief, when their only crime was to honestly follow their reason and intellect as best they could. Would we rather these folks lie to us, in order to make us feel more comfortable? Would we rather they be dishonest with themselves, or live in fear?
The big picture
If there really was one deity who demanded one particular interpretation of one particular holy book, it would be fair to conclude that such a deity has utterly failed to make themselves clear. The staggering numbers of devotees in each religion conclusively prove that humanity as a whole has no idea which holy book contains any more truth than any other. And that has always been the case throughout history. Any deity therefore who might be the author of one of these holy books has either failed to make themselves known in any meaningful way, or didn't care to. If one is to believe that the unfaithful and those who worship the wrong deity (which includes at least two thirds of the world's population no matter how you slice it) are to deserve punishment at the hand of this hidden deity, that makes this deity morally repugnant.
Perhaps you might argue that it is not the deity's fault if two thirds of the population lack the intelligence or good sense to understand the true message of the Bible, but given that this deity is said to have created all people and has a plan for their life, I beg to differ. At this point many people will insist that God allows us 'free will' and thus has wiped his hands of all responsibility. But God supposedly had no problem interfering with the free will of countless people in the Biblical text, so why start respecting it now? It just doesn't add up.
Finally, any thinking person would also need to conclude that even with all of this information, if the Biblical deity is the one true god, then being all-knowing he knew all of this in advance, and being all-powerful he could have changed it, but instead he chose to go ahead with this total disaster of a plan anyway.
I wonder what the world would look like if there was no deity behind any of the world's religions...
Culture
Another reason there are varying beliefs and belief systems around the world is because we are all influenced by the culture and environment we grew up in. Most religions survive by teaching their doctrines and customs to children when they are very young. The Bible itself tells us why:
"Train a child in the way that he should go, and when he is old he will not turn from it."This admission is quite disturbing if it is true. It essentially means the death of rationality and reason. Children do not have the reasoning capacity of an adult, and tend to be very willing to believe whatever they are taught. Why wouldn't they? Indeed, in some cases it is vital to their survival that they learn to trust their parents and teachers implicitly. Yet if they remain unable or unwilling to question anything they were taught, even after developing a sense of reason in later years, then of what use is that reason and intellect? Again, when it comes time to teach their own children, will they just repeat the cycle? I have witnessed this very thing in my own lifetime. Many people seem unwilling and even afraid to entertain the possibility that their own parents and teachers may have been mistaken. They go on to teach these same beliefs to their own children with unwavering conviction, having never undertaken any independent study or research of their own.
Proverbs 22:6 (NET)
A brief aside...
I have to stop here and note that many of you will no doubt object to this and say that you have questioned and tested your beliefs, and, just like 95% of other people who claim likewise, you have concluded that the beliefs your parents taught you are the right ones. That should give you pause. Especially if you were born into a Christadelphian family. The chance of being born into a Christadelphian family is incredibly tiny, and if you believe that Christadelphians alone have the truth, your birth must seem like a golden lottery ticket! Imagine if you weren't born a Christadelphian. Given the low numbers of Christadelphian converts, it's extremely unlikely you would have converted. So now if you remain a Christadelphian (which happens to be the path of least resistance), and are rewarded by God, wouldn't that effectively mean God chose your birth family and then rewarded you for going along with it? Sounds like a pretty sweet deal! Kinda sucks for everyone else though.
Moving on...
Of course, we know that the proverb is not strictly true in all cases. People can and do sometimes change their beliefs during their lifetime regardless of what they were taught when they were young. But such changes are rare. We may see this occur more and more in our times, but this is again due to a change in our culture. We have many more external influences, from ready access to books, public education, the internet, and travel. We don't need to look very far back in time to see that changing one's religious beliefs brought shame on their family, and on their community. Perhaps this sort of thing still occurs today. Perhaps among Christadelphians, particularly those esteemed more pious, and with a family name to uphold. Sadly, I have personally witnessed this as well (though not in my own family).
If people are so discouraged from seeking out other views, and so afraid of what they might find if they do, how shall any of them find the truth? Building walls around people's faith to protect the young and to keep the community together sounds noble at first, right up until you realise that all other religions are doing the same thing, and for the very same reason. Those who eventually do look over the walls may come face to face with other communities that look very much like their own, only with a different set of beliefs. It is natural when confronted with such opposition to try to win the opponent over to your side. A few will even succeed. Most will not. And so each religion grows in its own right. Each one convinced of its own truth. Each one comforted by the numbers of like-minded people surrounding them. Each one perhaps oblivious to the fact that they and their neighbours are more alike than they are different.
Like charges repel
It is tempting to think that others hold different beliefs simply because they have read the wrong material, or because they have been brainwashed with error from a young age. But if we too were taught our beliefs from a young age just like they were, how did we escape their plight? Maybe we didn't escape it. I wonder if they view us the same way. What do people from other religions think of Christadelphians? Have you ever wondered that? Spend some time on Google and look it up. I won't spoil it for you.
It may be confronting to come across other people's opinions of your own community. It feels personal, and the natural response is to get defensive. But try to resist that natural response. There is so much more to learn here. The people who write these opinions are real people just like you and me. Many were brought up to believe differently. Most are just as convinced they have the truth as you are. In fact many of them even call it "the truth", just like Christadelphians do. It's natural to want to recoil and see these people as somewhat alien. How dare they challenge your beliefs when you know you have the truth and you can prove it!
If you can, put aside your defensiveness and listen to the way they speak. Perhaps one of the reasons we react so strongly in these situations is because we unwittingly see a reflection of ourselves, and who we have become. We may not at first recognise the similarities, but we are seeing it from an outsider's perspective, perhaps for the first time. No matter what you think of those people, it is likely they are thinking the same things about you. Put yourself in their shoes. Imagine you were raised as a Catholic, or a Jehovah's Witness. How would that person view your current self as you are today?
If you could speak to a Hindu version of yourself, what message would you tell them? How would you persuade them you were right? If the roles were reversed, how would a Hindu change your mind?
Don't be afraid to ask questions
If your mind is made up and cannot be changed, think back to the child who was instructed in these ways and refuses to question when he or she is old enough to reason. Is that you?
Have you built walls around your faith to protect it from any external challenge? What is your faith afraid of? If everyone did that, would anyone ever learn anything new?
What frame of mind would you want a person of another faith to have, in discussions with you? Do you think you would do the same for them? I think you owe it to yourself to try.
Don't be afraid to learn. Don't be afraid to challenge your own beliefs. That is how you grow in understanding and wisdom. A strong faith or belief system is not one that is never tested. It is one that fears no challenge, and welcomes new discoveries. That means having the courage to change your mind. Follow the truth, wherever it leads. Accept the possibility that you may not have found it yet. What you discover will amaze you.